In a superconducting apparatus such as a superconducting motor and the like, a cryogenic refrigerant such as liquid nitrogen and liquid helium and the like (referred as “supplying refrigerant”) must be supplied to a cooling portion such as a superconducting field coil for maintaining a superconducting status of the super conducting field coil. Also, the refrigerant after use at the cooling portion (referred as “discharging refrigerant”) must be collected to a refrigerating machine. At this time, it is necessary to maintain the refrigerant supplied to the cooling portion in cryogenic condition, and necessary to reduce an amount of use of the refrigerant which is costly. For example, in order to supply the supplying refrigerant from the refrigerating machine on a stationary side to the superconducting motor which is rotating, the supplying refrigerant must be passed through a rotary joint connecting a fluid passage at a stationary portion and a fluid passage at a rotary portion, in which the stationary portion and the rotary portion are relatively rotating.
In this rotary joint, a seal device for sealing a fluid passage at relatively rotating communication passages with the fluid passage at the stationary portion and the fluid passage at the rotary portion, have a problem of the capability to seal the cryogenic refrigerant due to the cryogenic temperature, in order to seal the supplying refrigerant or the discharging refrigerant in at cryogenic temperature. Also, when the temperature of the supplying refrigerant rises, the superconducting function cannot be achieved without increasing of the amount of the supplying refrigerant, because it cannot be cooled to a predetermined cryogenic temperature. Therefore, there is a problem of increase in the amount of the supplying refrigerant to the cooling portion. When the supplying amount of the supplying refrigerant increases, a problem of the sealing capability of the seal device also occurs.
Further, it has been known that vacuum thermal insulation is excellent for thermal insulation at the time of supplying the supplying refrigerant. However, in order to perform the vacuum thermal insulation, it is difficult to maintain the supplying refrigerant at the cryogenic temperature without heightening a degree of vacuum of a space on an outer circumferential side enclosing the fluid passage. In order to maintain high vacuum for this vacuum thermal insulation, a vacuum seal device for shutting off ambient air is necessary. In this vacuum seal device, since the lubricating capability of seal faces are lost by the vacuum, the seal faces are worn out. As a result, the degree of vacuum which should be used for thermal insulation is lowered. There is a problem that the supplying refrigerant maintained at the cryogenic temperature cannot be supplied to the cooling portion due to a sealing capability of the seal device. Under such condition, because it is necessary to supply a large amount of the supplying refrigerant to the cooling portion in order to maintain the cooling portion at the cryogenic temperature, it becomes a problem that a running cost of the supplying refrigerant, which is costly, increases. Thus, an advantageous rotary joint is required.
In FIG. 9 of Japanese Patent Laid Open No. 2003-65477 (Patent Document 1) (although FIG. 9 is omitted here, numeral references in drawings of the Patent Document 1 are shown after the names of components), a cross sectional view of a cryogenic material transfer joint 26 for supplying the cryogenic fluid to a synchronous generating machine as “a synchronous machine comprising a gas transfer joint for cryogenic gas to a rotor provided with a superconducting coil” is shown. In this cryogenic material transfer joint 26, a tip end 158 of an insert tube 154 on the stationary side is fitted into an inner circumferential face of an inlet tube 156 in non-contact status to constitute a non-contact seal. However, in this non-contact seal, the insert tube 154 merely fits to the inner circumferential face of the inlet tube 156 in non-contact status. Therefore, when inlet cryogenic gas 157 supplied from a cryogenic cooling apparatus 190 flows into the inlet tube 156 through the insert tube 154, there is a risk that part of the cryogenic gas 157 flows into the inside of a cylindrical housing 186 from a gap between the insert tube 154 and the inlet tube 156 which are fitted in non-contact status.
Although the cylindrical housing 186 is maintained in vacuum condition, when the inlet cryogenic gas 157 flows into the cylindrical housing 186, the thermal insulation effect by vacuum condition decreases, because the degree of vacuum in the cylindrical housing 186 is lowered. As a result, because it is necessary to supply the large amount of the inlet cryogenic gas 157 to the cooling portion, the running const increases. Also, supplying large amount of the inlet cryogenic gas 157 to the cooling portion causes a constitutional problem that collection thereof is extremely difficult.
Also, because the cryogenic material transfer joint 26 has a constitution that high temperature cooling gas 164 flows in an annular space between an outer circumference of the cooling inlet tube 156 in which the inlet cryogenic gas 157 flows and a cooling outlet tube 166, there is a risk that the temperature of the inlet cryogenic gas 157 which flows in the cooling inlet tube 156 rises due to the high temperature cooling gas 164.
Also, because a motion gap seal 162 disposed in a cylindrical casing 168 is provided as the inlet cryogenic gas 157 flows on an inner circumferential side and the high temperature cooling gas 164 flows on an outer circumferential side, there is a risk that quality of material deteriorates by the cryogenic temperature to lower the sealing capability. Particularly, in the constitution of the cryogenic material transfer joint 26 which has low thermal insulation effect against the outside, because a large amount of inlet cryogenic gas 157 must be supplied to a super-conducting (SC) coil winding, there is a risk that the motion gap seal 162 deteriorates rapidly.
Further, although it is described that a magnetic fluid seal 176 mounted in a cylindrical hosing 196 prevents the return gas 164 from leaking (refer to paragraph 0046), this structure is unclear. In the magnetic fluid seal 176 known so far, when the inside of the cylindrical housing 186 is vacuumized, the magnetic fluid is sucked into the cylindrical housing 186 so that the sealing capability of the magnetic fluid seal 176 is lowered. For this reason, there is a possibility that the outside air flow 177 flows into the cylindrical housing 186 through the magnetic fluid seal 176, so that the degree of vacuum in the cylindrical housing 186 is lowered. When the degree of vacuum in the cylindrical housing 186 is lowered, the thermal insulation effect of the inlet cryogenic gas 175 cannot be obtained. In an ordinal magnetic fluid seal, it is difficult to maintain this high degree of vacuum.
In a conventional sealing means including the magnetic fluid seal device, because a space on the sliding face is vacuumized so that a lubricant on the sliding face is sucked, the sliding face is worn out. As a result, the air flow 177 and further retuning gas gradually flow into the cylindrical housing 186 through a space between seal faces, so that it becomes difficult to maintain the inlet cryogenic gas 157 below 30° K of the cryogenic temperature. When the inlet cryogenic gas 175 cannot be maintained below 30° K, the superconducting effect of the superconducting coil (coil winding 34) cannot be achieved. Therefore, more flow amount of the inlet cryogenic gas 157 than ordinary flow amount necessary for the superconducting coil must be supplied to the superconducting coil side. In this real scene, because the cooling fluid such as helium and the like are costly, running costs of the synchronous generating machine and the like are increased.
Further, in FIG. 1 or FIG. 3 of Japanese Patent No. 3306452 (Patent Document 2) (although Figs. are omitted here, numeral references in drawings of the Patent Document 2 are shown after names of components), cross sectional views of constitutions, in which a liquid helium injection pipe (1) is inserted into an inner circumferential face of a protruding portion (10) covered by a vacuum layer (2) in the similar way as the Patent Document 1, are shown. In the constitutions, a space is formed between the inner circumferential face of this inserted protruding portion (10) and an outer circumferential face of the liquid helium injection pipe (1). The liquid helium is sealed to be prevented from leaking to the outside by a seal (4) for shutting off a space on an outer circumferential side communicating with the space formed between the inner circumferential face of the inserted protruding portion (10) and the outer circumferential face of the liquid helium injection pipe (1). However, even this constitution of the Patent Document 2, as the Patent Document 1, it is difficult to seal the liquid helium of cryogenic temperature by the conventional seal (4) as similar with the patent document 1, because the liquid helium is cryogenic temperature. It cause various problems on the seal face to seal the liquid helium by the mere seal device with the ordinary constitution. Also, although it has the constitution that the vacuum layer (2) is encapsulated in a space on the outside of the pipe, the thermal insulation effect for a long period to the liquid helium cannot be achieved, because in the encapsulation constitution, the degree of vacuum is decreased with time.
Also, in the constitution that the inlet tube 156 is fitted to the insert tube 154 on the stationary side as shown in the Patent Document 1, or in the constitution that the liquid helium injection pipe (1) is fitted to the protruding portion (10) at the tip end of the rotor towards a bore center (19) (introducing bore) in an axial direction as shown in the Patent Document 2, it becomes difficult to fix the inlet tube 156 on the rotor side or the protruding portion (10) at the tip end of the rotor, so that there is a risk that, when the inlet tube 156 or the protruding portion 10 of the tip end of the rotor is in contact with the relative face, it slides with the insert tube 154 on the stationary side or the liquid helium injection pipe (1) to occur abrasion powders. Also, in this constitution, it is difficult to maintain the degree of vacuum. Further, when a plurality of liquid helium injection pipes (1) is necessary in response to a number of superconducting magnetic field coil, the rotor is complicated in response to numbers thereof to complicate the constitution of the seal device.    Patent Document 1: Japanese Patent Laid Open No. 2003-65477    Patent Document 2: Japanese Patent No. 3306452